The present invention relates to valves to be installed for example in the fuel gas feed channel for a burner to regulate the rate of flow of fuel gas into the burner and to thereby properly maintain the fuel-to-air ratio during combustion. More particularly, the invention relates to a flow rate regulating valve comprising a valve casing disposed substantially at right angles to a fluid channel, a valve member movably fitted in the valve casing and a manipulating portion for moving the movable valve member from outside the valve casing so that the degree of opening of the fluid channel can be adjusted to regulate the flow rate by moving the valve member.
Observation of combustion of gas indicates that unless a proper fuel-to-air ratio is maintained, the fuel-air mixture is likely to be outside the explosion limits, favoring inadvertent extinction of fire in the burner and possibly leading to a hazardous situation that the furnace is filled with a raw gas. Use of natural gas as the fuel involves a still greater hazard, because the gas has narrow explosion limits. In contrast, when the fuel-to-air ratio is maintained properly throughout the entire range of low combustion to high combustion, complete combustion will result which serves to inhibit nitrogen oxide emissions, a cause of air pollution, and also to achieve improved combustion efficiency for economical use of energy.
Accordingly, flow rate regulating valves for controlling combustion must have such flow rate characteristics that when the amount of combustion is altered, the fuel gas supply can be regulated in conformity with a change in the combustion air supply required by the altered amount of combustion so as to maintain a proper fuel-to-air ratio.
Supposedly, valves of varying flow rate characteristics adapted for varying types of burners and fuels may be prepared so that an appropriate valve can be used selectively for the particular burner and fuel desired, but the manufacturing cost will then be prohibitive. Further it is possible to replace the flow rate regulating valve to provide different flow rate characteristics when the burner or fuel is changed, but this is very inconvenient and uneconomical for practical use. It is therefore required that the valve for regulating the flow rate of gas be freely variable as desired in its flow rate characteristics.
In order to fulfil the foregoing requirements, a gas flow rate regulating valve has already been provided which includes a third member for altering the opening area of the flow channel to give variable flow rate characteristics. However, because the regulating valve is so adapted that the area of opening of the flow channel is altered at a linearly (i.e. linear functionally) variable change rate, the flow rate characteristics thereof, although variable, are limited to a narrow range of alterations. In other words, the desired flow rate characteristics are not always available.
Another type of gas flow rate regulating valve including such third member is also known which further incorporates cam means for moving the third member in operative relation to the movement of a movable valve member, such that the rate of variation in the opening area of the fluid channel is altered relative to the opening of the flow channel as adjusted by the movement of the movable valve member. The flow rate characteristics of this valve are freely variable, since the area of opening can be altered by the movement of the movable valve member and also by the movement of the third member. However, the cam means incorporated makes the valve complex in construction and costly to manufacture. When worn away during use, moreover, the cam means produces a play in the movement of the third member and needs replacement to maintain the desired controlling function over a prolonged period of time. The valve therefore requires a high running cost. Furthermore, the flow rate characteristics to be determined by adjusting the cam means are not settable with high precision.